Do Speak to a manager on duty, preferably before you check out.  Spa professionals care deeply about customer satisfaction and need to know about areas of concern or needed improvement.  By voicing your concern, you will allow the spa to address and correct any issues, and you give them the opportunity to make it right.  You are welcome to contact the SA Spa Association if your complaint is not suitably handled and they in turn will contact the spa and ensure the situation is addressed.